Charles e



(No Model.)

0. E. SCRIBN'ER. SYSTEM OF GUBRENT SUPPLY FOB. TELEPHONES.

Patented May 5, 1896.

ANDREW @GRMAMfnUTOMYflQWASmNGXON Dc UNITED STATES PATENT FFICEe CHARLESE. SCRIBNER, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE WESTERN ELECTRICCOMPANY, OF SAME PLACE.

SYSTEM OF CURRENT SUPPLY FOR TELEPHONES.

SPECIFICATION forming part of Letters Patent No. 559,616, dated May 5,1896.

Application filed January 8, 1895. Serial No. 534,211. (No model.)

To all whom it may concern.-

Be it known that I, CHARLES E. SCRIBNER, a citizen of the United States,residing at Chicago, in the county of Cook and State of 5 Illinois, haveinvented a certain new and useful Improvement in Systems of CurrentSupply for Telephones, (Case No. 373,) of which the following is a full,clear, concise, and exact description, reference being had to the toaccompanying drawings, forming a part of this specification.

My invention relates to telephone-exchange systems in which thesubstation-microphones are supplied with current from a common sourcelocated at the central station or other convenient point. Its object isto provide a simple and efficient system for supplying current in whichcross-talk or telephonic interferences between different lines of thesystem so shall be eliminated and the difference of potential betweenthe terminals of either of two connected lines shall be renderedindependent of the resistance or electrical condition of the other line.A secondary object is to provide forindependent signals in the circuitsof telephone-lines adapted to be automatically operated by thealteration of the circuits at the substation in the use or disuse of thetelephone.

In my invention I interpose a condenser in the condo ctor ordinarilyemployed for uniting telephone-lines in a telephone-switchboard, and Iconnect the common source of current supply with the severed portions ofthis conductor through. impedance-coils. A steady current is thuspermitted to flow from the source of supply through either impedancecoilto the corresponc'ling portion of the cond uctor uniting the lines, andthence through the substation-microphones included in the lines. Thevariations caused by one substation-microphone in the current through itare propagated, through the medium of the condenser in the conductoruniting the lines, through the other line-wire and the telephone 50tcrnal resistance the Volume of current in in its circuit, theirtransmission through the either line is independent of the resistance inthe other line, since the conductors of the line are separated as to thesteady currents in their circuits by the condenser. Hence if a short andlong line be coupled together the instruments in the long andhigh-resistance line are not deprived of current for their properoperation by the shunt-path through the lower-resistance line. At thesame time the electrostatic impulses which are propagated from one linethrough the condenser to the other line are found to be but slightly dependent, within certain wide limits, upon the resistance in theircircuit.

It has been found desirable in practice to provide signals in connectionwith the linecircuits which shall be automatically controlled by theposition of the telephonic apparatus at the substations, theirindicators being displayed or concealed as the telephone is brought intouse or returned to its normal position. Such signals ordinarily comprisea line-signal permanently connected with each line, which is adapted todisplayits indicator when the telephone is removed from its switch-hookfor use, and a pair of clearingout signals in each loop-conductor foruniting telephone-lines, the two clearing-out signals of eachplug-circuit being adapted to operate independently, each serving tonotify the operator of the replacement of the telephone of the line withwhich it is more directly connccted.

A feature of my invention consists in the combination, with thebefore-described system of current distribution, of line and cleaning-out signals. I connect with each line, as heretofore, aline signalor annunciator of considerable resistance, the free terminal of thesignal being connected to one pole of the source of electric currentwhich it is designed to employ in supplying the substation-microphones;and I provide the impedance-coils of the currentsupply system withsuitable mechanism for operatingindicators, thus converting them intosignaling instruments.

The impedance-coils are constructed to have comparatively low ohmicresistance,whereby, when they are brought into circuit with telephonedines, the current through the line-sig- IOO nal is shunted and thelatter returns to its normal position.

In the idle condition of the line the linesignal remains inert, theline-circuit being open at the substation. WVhen the apparatus there isbrought into position for use, as by removing the telephone from itsswitch-hook, the line-cireuit is closed through the telephone andmicrophone and the line-annullciator is operated by the current whichfinds circuit through it from the common battery or other source ofsupply. WV hen connection is made with the line in the usual way, theline signal is shunted and becomes again inert, the clearing-out signalis displayed, and suitable current for operating the substationmicrophone is put upon the line. Upon the return of the substationapparatus to its normal position the clearing-out signal signifies thiscondition.

Hitherto it has been necessary to include the clearing-out signalsdirectly in the linecireuit, in which position their impedance andresistance have been detrimental to te1e phonic transmission. In thearrangement which I have invented, however, it will be noted thatindependence of operation of the signals is secured, while theirresistance is eliminated from the telephonic circuit. At the same time asimple and particularly efiective mode of rendering the line-signalinert and insuring its return to its normal condition is provided.

I am aware that it is not new in the art of telephony to supply-currentfor operating substation-microphones to different lines from a commonsource through different impedancecoils, the lines being united by acontinuous conductor; and also that it is not new to connect a source ofcurrent with two different portions of a continuous line-circuit throughdifferent signals, a condenser being interposed in the circuit betweenthe points of connection of the different signals in, a system forsignaling purposes alone. I believe myself to be the first, however, todiscover the possibility of producing in a telephone-line a steadycurrent by connecting a source of sup ply through a coil havingsufficient impedance to prevent the passage of telephonic currents andof permitting variations in the current of the first line andpropagating them in another line through the medium of a condenser, andto bring the condenser and signals into such relation that they exercisetheir functions cooperatively in the diit'erent systems.

My invention is illustrated in the accompanying drawings, in which-Figure 1 represents the circuits of the system of current supply alone,the two substations being shown in a continuous metallic circuit whichis provided with circuits and apparatus in accordance with my inventionfor supplying current to the substation-microphones. Fig. 2 representsthe combined system of current supply and automatic signaling, theapparatus being shown in connection with the usual mechanism of atelephone-switchboard.

In the simple system shown in Fig. 1 each of the substations A and B isequipped with a microphone c and a telephone 0, these instruments beingincluded in series in a metallic circuit 1 2. A condenser d is includedin the conductor 1 at a point which may be the central. section. Fromeach side of the condenser branches 3 at are taken, includingimpedance-coils e and e. These branches are connected with one pole of abattery f, whose other pole is connected by a conductor 5, includinganother impedance-coil, with the line-wire 2. As many line-circuits maybe connected with the single battery f as desired, the connections beingtaken through branches similar to 3, 4-, and 5, includingimpedance-coils. The condenser cl may be oi one microfarad capacity andthe impedancecoils may each be of ten or fifteen ohms resistance, ormore, if desired.

Obviously the battery f will create through each substation apractically continuous current, the current in either circuit dependingsolely upon the resistance of that circuit. It sounds are made in onemicrophone, as c, at station A, the current in the line-circuit to thatstation is varied in accordance with the varying resistance of themicrophone. The fluctuations of this current do not appear to traversethe impedance-coils c and 6 but rather to be absorbed in condenser d andpropagated through the medium of the latter through the circuittostation 13. The soundwaves impinging upon microphone c at station A arethus reproduced in the telephone at station E. Since no perceptiblefluctuation takes place in the current through the impedance-coils e, c,and 6 the battery f may have a considerable internal resistance withoutthe occurrence of cross-talk between the diiferent telephone circuitsconnected with it in common.

Referring now to Fig. 2, similar telephonic appliances are indicated atthe substations A and 13, together with a signal'bell 0 a condenser c incircuit with it, and a telephone switch-hook c, from which the telephoneis normally suspended,the switch being adapted to connect the telephoneand the bell alternately in the line-circuit as the telephone is removedfrom or replaced upon its support. The line-wire 1 from station A isconnected with one line-contact of a spring-jack g in atelephonc-switchboard at the central station and with one terminal of asignaling instrument'h, whose other terminal is connected with one poleof the common battery f. This signal should be of moderately highresistanceas, for example, five hundred oh1ns and should be soconstructed as to fail to re spond to alternating currents such asemployed for operating the substation bells. The line conductor 2 fromstation A is likewise connected with a line-contact of springjack g, andis also connected to earth through YIO an impedance-coil 6 Theline-circuit from station E is connected with similar apparatus in theswitchboard.

At the switchboard a number of plugs, with their accessory circuits andswitches, are provided, but one pair being shown, however. The plugs t'and t" are constructed each with two contact-points 7t and 7t, adaptedto register with the two line-contacts of a springjack. The tips 7a ofthe two plugs are united by a conductor 6 and the sleeves 7; by aconductor 7. A condenser d is included in the conductor (3. From thesevered portions of this conductor branches 3 and a are taken to onepole of batteryf, the other pole of the battery being connected toearth. In the branches 3 and a. signals 6 and e are included, theelectromagnets of the signals being constructed to have sufficientimpedance to permit them to perform the functions of the impedance-coils described in connection with Fig. 1. An operators listening-keyZ is furnished to enable the operator to connect her telephone set mwith the plugcircuit (5 7, and a calling-key 7t for looping a generator0 of signaling-current, suitable for opcratin g bells 0 into circuitwith plug 1'".

W hen the subscriber at station A desires to converse with thesubscriber at another substation-as, for example, at station B-heremoves his telephone 0 from switch-hook c, thus permitting the latterto close the hitherto open circuit between conductors 1 and 2 throughthe telephone c and microphone 0. Current from battery f then findscircuit through signal it and line conductor 1 to line 2, and thencethrough the impedance-coil c at the central station. The signal is thusexcited and indicates the call to the attendant, who in response insertsplug 1' into the springjack g of the corresponding line, at the sametime bringing the telephone minto connection with the plug-circuit.Battery f is now provided with a circuit of much lower resistancethrough signal '6 and conductor 6 of the plugcircuit to the line-wire 1,returning through the line 2 and impedance-coil c The current suitablefor the operation of the microphone is thus obtained at the substation.In the new arrangement of the circuits the impedance-coil e of lowresistance is in shunt of the signal it of high resistance, and thelatter, being practically short-circuited, becomes inert and returns toits normal position. Having learned thesubscribers order, the operatorinserts plug 7; into spring-jack of line to station B and depresses theplunger of callingkey n, thus ringing bell c at station E. lVhen thesubscriber at this station has responded and has removed his telephonefromits switchhook, the telephonic appliances at the substations areunited in a complete metallic circuit, including condenser cl, bothstations bein g supplied with current from battery f. Conversation maythen take place, as described in connection with Fig. 1. When eithertelephone is replaced upon its switchhook, the circuit of battery fthrough that line is interrupted at condenser 0 whereby thecorresponding clearing-out signal 6 or e becomes demagnetized andreturns to its inert position, displaying a suitable signal to indicateto the operator the position of the apparatus at the substation. Thedisplay of both signals may be interpreted as signifying that theconversation is terminated and the connection between the lines may beremoved.

It is found in practice that with the condenser connected in the circuitof the lines between the points of supply of current to them it ispossible to employ impedance-coils c c of less resistance than would bepermissible with a continuous conductor in place of the condenser, noappreciable interference between different telephonelines connected withthe common battery being noticeable with low-resistance impedance-coilsarranged as herein described. My invention therefore permits the use ofa battery of much lower electromotive force than would be necessary toprovide the proper volume of current for operating thesubstation-transmit-ters if the impedance-coils e and 6 were of highresistance, and thus accomplishes transmission with a minim umexpenditure of energy in the system of distribution.

I claim as new and desire to secure by Letters Patent 1. The combinationwith a telephone-circuit, of a microphone and a telephone in thecircuit, a condenser included in the circuit between the microphone andthe telephone, and a source of electric current for supplying themicrophone connected through a resistance-coil with that portion of theline including the microphone, substantially as described.

2. The combination with a telephone-line, of a microphone included inseries in the telephone-circuit at each terminal station of the line, acondenser in the line intermediate of the two stations, a source ofelectric current and a connection from said source of current through animpedance-coil to the line at each side of the condenser, substantiallyas described.

3. The combination with a metallic-circuit telephone-line, of amicrophone and a tele phone in series in the line at each of theterminal stations thereof, a condenser in one side of the lineintermediate of the stations, a source of electric current, two branchesfrom one pole thereof through impedancecoils to the same side of thetelephone-line at each side of the condenser therein, and a branch fromthe other pole of the battery to the other side of thetelephone-circuit, substantially as described.

4;. The combination with a source of electric current, of severalcomplete telephonecircuits, each including a microphone at each of itsterminal stations, a condenser in each circuit intermediate of theterminal stations, branches from each side of each condenser to the samepole of the said source of current, and a low-resistance impedance-coilin each of said branches, substantially as described,

5. The combinationwith two united tele-' phone-lines, of a microphoneand a telephone at the substation of each line, and means for openingthe line-circuit or closing it through theline-circuit orclosing itthrough the microphone, a source of electric current permanentlyconnectedwith the line through a con- I ductor includingahigh-resistance signaling instrument, a link conductor for establishingconnection between lines, a branch from said source of'curren-t to thelink conductor, and a signaling instrument of comparatively lowresistance included in the said branch, Whercby the high-resistanccsignaling instrument is practically shoit-circuited by thelow-resistance instrument and the latter is adapted with the line.

7. In oombination,two telephone-lines each provided With a microphoneandtelephone at its substation and with a switch adapted to interrupt theline-circuit or to close it through the microphone, a common source ofcurrent. a branch from one pole of said source of current to each linethrough a signaling instrument of high resistance, a link conductorforuniting the lines, a condenser included therein, a branch fromthe samepole of the said source of current to each side of the condenser, and asignaling instrument of comparatively low resistance included in each orsaid branches, whereby When connection is made between'the lines currentis supplied toeach line for operating its transmitter, the line-signalof each line is practically shortcircuited, and a clearing-out signal isbrought into connectionwith each line, substantially as described.

- In Witness whereof I hereunto subscribe in 3

